1. Field of the Invention
The present invention relates to an image forming method, an image processing method and an ink jet recording apparatus, and more particularly to an image forming method, an image processing method and an ink jet recording apparatus in case of employing a recording material of a specific color different in hue from basic colors.
2. Related Background Art
Together with the recent pervasiveness of information processing apparatus such as personal computers, recording apparatus as an image forming terminals has also shown remarkable development. Among various recording apparatuses, an ink jet recording apparatus, which discharges an ink from a discharge port for recording on a recording medium such as paper, cloth, plastic sheet, OHP sheet etc., has excellent characteristics such as a non-impact recording method of low noise level, an ability for a recording operation of a high density and a high speed, an ability of easily attaining a color recording and an inexpensiveness, and has now become a main stream of the recording apparatus for personal use.
The ink jet recording apparatus has basically adopted a color reproduction by a subtractive color mixing utilizing inks of yellow, magenta and cyan which are three primary colors in printing. More specifically, an image of an orange or red area for example is formed by mixing yellow and magenta colors, also an image of a green area is formed by mixing yellow and cyan colors, and an image of a blue or violet area is formed by mixing magenta and cyan colors.
The advancement of the ink jet recording technology has stimulated developments of recording toward a higher resolution, a higher image quality, a color reproduction and a more inexpensive image formation, and has also contributed significantly to spread the recording apparatus even to personal users, combined with the spreading of personal computer and digital cameras (not only those in single units but also those integrated with other apparatuses such as cellular phones). However, because of such wide pervasiveness, a further improvement in the image quality is being requested even from personal users, and various improvements are being made in order to respond to such requirements.
One of such improvements is a method of employing a black ink in addition to the inks of three primary colors and executing an UCR process of extracting a black component K from the data Y, M and C of the yellow, magenta and cyan colors for replacement by the black ink and removing thus replaced C, M and Y color components, thereby improving a contrast and achieving a stable reproduction of neutral colors. Another method employs, in addition to the yellow, magenta, cyan and black inks, inks of a light cyan color and a light magenta ink thereby reducing granularity of the dots formed by ink deposition onto a recording medium and improving gradation. Also Japanese Patent Application Laid-Open Nos. 2003-39711 and 2003-80682 disclose a technology of assigning a larger number of gradation levels to the light cyan ink and the light magenta ink than in other inks, thereby reducing the granularity not only in a highlight area formed by such light colored inks but also in a medium density area where a dense colored ink and a light colored ink are present together. However, since there is a limitation in the color reproduction by the inks of three colors of yellow, magenta and cyan (or four colors also including black), or even by the inks including light inks of same hues, there is proposed a method of using inks of other colors.
In certain industrial fields such as lithographic printing or dyeing, there may be employed an ink of so-called “specific color”. However, such ink is intended specifically for reproducing, in a mass-produced specified image, a specific color (which cannot be reproduced or is difficult to reproduce with the aforementioned four colors and similar colors, such as a metallic color or cobalt blue), and is not intended for use in a general color reproduction.
On the other hand, as a method for realizing a wider image formation, it is also proposed to use, in addition to yellow, magenta and cyan mentioned above, inks of intermediate hue angles in the color space such as red, green or blue, thereby improving the color development and expanding the color reproduction range.
For example Japanese Patent Application Laid-Open No. H11-69176 discloses, for expanding a color range for example in a printer for obtaining a color reproduction of a higher accuracy and a higher image quality, a technology of color-converting television image signals RCRT, GCRT, BCRT by a three-dimensional look-up table (LUT) into C′, M′, Y′, then distributing or converting these data into data of six primary colors C, M, Y, R, G, B by a distribution function utilizing predetermined three variable, and executing a recording with recording materials of such six colors.
Also Japanese Patent Application Laid-Open No. 2001-138552 discloses a technology of employing an orange ink which is in an intermediate area between Y and M in the color space and a green ink which is in an intermediate area between Y and C, for the purpose of expanding the color reproduction range.
Also Japanese Patent Application Laid-Open No. 2003-34765 discloses a technology of employing an orange ink which is in an intermediate area between Y and M in the color space, a green ink which is in an intermediate area between Y and C, and a violet ink which is in an intermediate area between M and C, for the purpose of expanding the color reproduction range.
Now, in consideration of a historical evolution that the wide popularity of the recording apparatus has resulting in a requirement for a higher image quality, then improvements made for meeting such requirement have created new demands and a further improvement in the image quality is being requested, it will be obvious that an image quality far exceeding the photographic quality will also be requested.
In order to realize an image quality far exceeding the photographic quality, it is extremely effect to achieve a clarity, a transparent impression and a stereo impression, and an approach toward such image quality is to assimilate an image formed on a positive film. An image forming on a positive film is a transmission image which functions on the human visual sense by a light transmission from the rear side, and is therefore considered to create a transparent impression and a stereo impression. It is therefore considered effective for further improving the image quality, to realize an image quality causing a transparent impression and a stereo impression, equivalent to those of the transmission image, to the visual sense, in a reflective image.
Consequently, the present inventors have made a comparison of an image formed on a positive film and an image formed with a printer of a wide color reproduction range. An example will be explained in the following.
FIG. 1 shows a plotting of gamuts of an ink jet recording apparatus and a positive film on an a*b* plane of a CIE-L*a*b* system. In FIG. 1, a solid area surrounded by a solid line indicates gamut of the ink jet printer, and an area indicated by points indicates gamut of the positive film. As will be apparent from FIG. 1, the positive film has a larger gamut than in the ink jet printer, in areas of Y to R, G and B.
FIGS. 2A and 2B show the methods for calculating the gamut data shown in FIG. 1. In FIG. 2A, the gamut data of the positive film are obtained by scanning 84 positive films of 8 categories of mountain photos (sunset scenes), sceneries (sea and mountain), flowers, fishes, birds, butterflies, folk dresses and computer graphics. There were employed a scanner Nexscan F4200 manufactured by Heidelberg Gmbh, a color space Wide Gamut RGB. In the Wide Gamut RGB, a white point is represented by D50, and three RGB primary colors have x-y chromaticity values of R (0.73, 0.27), G(0.12, 0.83) and B(0.16, 0.02). A conversion from the Wide Gamut RGB to XYZ can be executed according to:X=0.7165×R+0.1010×G+0.1468×B Y=0.2587×R+0.7247×G+0.0166×B Z=0.0000×R+0.0512×G+0.7739×B. Conversion from XYZ to L*a*b* was executed according to the CIE definition.
Also in FIG. 1B, the gamut data of the ink jet printer was calculated employing a color patch printed with a recording apparatus Pixus 950i manufactured by Canon Inc. on a recording paper PR-101 manufactured by Canon Inc., and measured with a spectrophotometer Spectro Lino manufactured by Gretab-Macbeth Inc. The used printer executes an image formation with yellow, magenta, cyan, black, light cyan and light magenta colors, and provides a gamut smaller than the gamut of a record obtained from a silver halide-based positive film (referred to as “positive film”) shown in FIG. 2A. As shown in FIG. 1, the color reproduction range is deficient particularly in the areas of specific colors such as red, green and blue.
Therefore, a color reproduction was tried by employing recording materials of the specific colors (red and green inks) in addition to the recording materials of other colors (for example yellow, magenta, cyan and black) in same amounts of application. As a result, the color reproduction range was still inferior to that of the positive film though it was expanded in red and green areas, and the difference from the color reproduction range of the positive film was different in respective colors. In the experiment, such difference was larger in the green area than in the red area. It is therefore necessary to widen the color reproduction range even if it is still smaller than that of the positive film.
Based on the foregoing, in order to obtain a color reproduction range of the printer closer to the color reproduction range of the positive film, it is not enough to add the recording material of the specific color in the same manner as the recording materials of other colors, and particularly in a specific color where the difference is large from the color reproduction range of the positive film, it is necessary to employ a different application amount in consideration of such tendency.
Therefore, the present inventors have recognized, in order to expand the color reproduction range appropriate on the a*b* plane in an ink jet recording apparatus and to realize an image quality having a high reproducibility in the transparent impression and stereo impression taking an image of a positive film as a guideline, that an addition of a specific color ink in the same manner as the inks of other color is not enough and that an image design optimum for the recording material of the specific color (such image design including a selection of a recording material of a specific color having appropriate characteristics (lightness and chroma) and an optimum image process and an optimum dot arrangement process exploiting the characteristics of such recording material of the specific color) is effective.